#include <bits/stdc++.h>
#define yes cout<<"YES\n"
#define no cout<<"NO\n"
#define int long long
#define ff first
#define ss second
#define pb push_back
#define y1 zildjian
#define left radio
#define right head
using namespace std;
const int N = 2501;
const int INF = 1e18;
const int mod = 1e9+7;
const int mod1 = 998244353;
mt19937_64 rng(chrono::steady_clock::now().time_since_epoch().count());
int n,m;
int a[N][N];
int del[N][N];
bool available(int w, int h, int i, int j){
if(i+w-1 > n) return 0;
if(j+h-1 > m) return 0;
for(int k = i;k<i+w;k++){
for(int l = j;l<j+h;l++){
if(!a[k][l]) return 0;
}
}
return 1;
}
void upd(int w, int h, int i, int j){
for(int k = i;k<i+w;k++){
for(int l = j;l<j+h;l++){
del[k][l] = 1;
}
}
}
void clear_del(){
for(int i = 1;i<=n;i++){
for(int j = 1;j<=m;j++){
del[i][j] = 0;
}
}
}
bool check(int w, int h){
// cout<<w<<' '<<h<<'\n';
clear_del();
for(int i = 1;i<=n;i++){
for(int j = 1;j<=m;j++){
if(a[i][j]){
// cout<<w<<' '<<h<<' '<<i<<' '<<j<<' '<<available(w,h,i,j)<<'\n';
if(!available(w,h,i,j)){
continue;
}
else{
upd(w,h,i,j);
}
}
}
}
bool ok = 1;
for(int i = 1;i<=n;i++){
for(int j = 1;j<=m;j++){
if(a[i][j] && !del[i][j]){
ok = 0;
break;
}
}
if(!ok) break;
}
return ok;
}
bool ok(int ar){
for(int w = 1;w*w<=ar;w++){
if(ar%w == 0){
int h = ar/w;
if(check(w,h)) return 1;
if(check(h,w)) return 1;
}
}
return 0;
}
void solve(){
cin>>n>>m;
for(int i = 1;i<=n;i++){
for(int j = 1;j<=m;j++){
char x;
cin>>x;
a[i][j] = x-'0';
}
}
int ans;
for(int i = 1;i<=n*m;i++){
if(ok(i)) ans = i;
}
cout<<ans<<'\n';
}
signed main(){
// freopen("bootfall.in","r",stdin);
// freopen("bootfall.out","w",stdout);
ios_base::sync_with_stdio(0);
cin.tie(nullptr);
// cout.tie(nullptr);
int t = 1;
// cin>>t;
for(int i = 1;i<=t;i++){
// cout<<"Case "<<i<<": ";
solve();
}
}
